The present invention generally relates to techniques for operating a disk drive apparatus. More particularly, the present invention provides techniques for reading and writing information onto a hard disk drive that compensate for flow induced vibrations, commonly called disk flutter. Merely by way of example, the present invention is implemented using vertically offset spring extensions (or hinges) in a head suspension assembly, but it would be recognized that the invention has a much broader range of applicability.
A hard disc drive (HDD) unit generally uses a spinning storage medium (e.g., a disk or platter) to store data. A read-write head is positioned in close proximity to the spinning storage medium by a Head Stack Assembly (HSA). Mounted on the HSA, a suspension assembly commonly includes a base plate, a load beam, and a flexure trace gimbal to which a slider is mounted. The slider supports the read-write head element. The load beam is generally composed of an actuator mounting section, a spring region, and a rigid region. The spring region gives the suspension a spring force or preload counteracting the aerodynamic lift force created by the spinning medium during reading or writing. A gimbal is mounted at the distal end of the load beam and supports the slider allowing the head to have pitch and roll movement in order to follow the irregularities of the disk surface.
Demand generally requires increased HDD storage capacity, which generally compels higher data track densities for the storage medium. Furthermore, the demand for faster rates of data seeking and accessing also leads to higher rotational speeds. A significant obstacle associated with increasing rotational speeds and storage capacity is often head positioning accuracy as the head flies above the spinning storage medium.
A significant obstacle to head positioning accuracy is disk flutter. Disk flutter is an aero-elastic instability induced by the coupling of the spinning storage medium and the air surrounding the media resulting in disk vibration modes. These flow induced vibrations can physically cause an off-track misalignment of the head to the desired track resulting in failure to access or write data on the right track. Problems associated with disk flutter become more intolerable with higher track densities and disk rotation speeds.
Accordingly, novel solutions for operating hard disk drives to substantially reduce off-track misalignment induced by disk flutter are needed.